Xiubin Gu

Shigella flexneri regulates tight junction-associated proteins in human intestinal epithelial cells

Shigella spp. are a group of Gram‐negative enteric bacilli that cause acute dysentery in humans. We demonstrate that Shigella flexneri has evolved the ability to regulate functional components of tight junctions after interaction at the apical and basolateral pole of model intestinal epithelia. In the regulation of tight junctional protein assemblies, S. flexneri can engage serotype‐specific mechanisms, which targets not only expression, but also cellular distri‐bution and membrane association of components of tight junctions. Distinct mechanisms resulting in the regulation of tight junction‐associated proteins are initiated after either apical or basolateral interactions. S. flexneri serotype 2a has the ability to remove claudin‐1 from Triton X‐insoluble protein fractions upon apical exposure to T‐84 cell monolayers. S. flexneri serotype 2a and 5, but not the non‐invasive Escherichia coli strain F‐18, share the ability to regulate expression of ZO‐1, ZO‐2, E‐cadherin and to dephosphorylate occludin. The disruption of tight junctions is dependent on direct interaction of living Shigella with intestinal epithelial cells and is supported by heat‐stable secreted bacterial products. Intestinal epithelial cells have the ability to compensate in part for S. flexneri induced regulation of tight junction‐associated proteins.

Interleukin-2 Receptor β Subunit-dependent and -independent Regulation of Intestinal Epithelial Tight Junctions

Interleukin (IL)-15 is able to regulate tight junction formation in intestinal epithelial cells. However, the mechanisms that regulate the intestinal barrier function in response to IL-15 and the involved subunits of the IL-15 ligand-receptor system are unknown. We determined the IL-2Rβ subunit and IL-15-dependent regulation of tight junction-associated proteins in the human intestinal epithelial cell line T-84. The IL-2Rβ subunit was expressed and induced signal transduction in caveolin enriched rafts in intestinal epithelial cells. IL-15-mediated tightening of intestinal epithelial monolayers correlated with the enhanced recruitment of tight junction proteins into Triton X-100-insoluble protein fractions. IL-15-mediated up-regulation of ZO-1 and ZO-2 expression was independent of the IL-2Rβ subunit, whereas the phosphorylation of occludin and enhanced membrane association of claudin-1 and claudin-2 by IL-15 required the presence of the IL-2Rβ subunit. Recruitment of claudins and hyperphosphorylated occludin into tight junctions resulted in a more marked induction of tight junction formation in intestinal epithelial cells than the up-regulation of ZO-1 and ZO-2 by itself. The regulation of the intestinal epithelial barrier function by IL-15 involves IL-2Rβ-dependent and -independent signaling pathways leading to the recruitment of claudins, hyperphosphorylated occludin, ZO-1, and ZO-2 into the tight junctional protein complex.